Re: HTTP/2 and TCP CWND
Wesley Eddy <wes@mti-systems.com> Fri, 19 April 2013 04:11 UTC
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Date: Fri, 19 Apr 2013 00:08:44 -0400
From: Wesley Eddy <wes@mti-systems.com>
Organization: MTI Systems
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To: Nandita Dukkipati <nanditad@google.com>
CC: Patrick McManus <mcmanus@ducksong.com>, Gabriel Montenegro <Gabriel.Montenegro@microsoft.com>, Roberto Peon <grmocg@gmail.com>, "Simpson, Robby (GE Energy Management)" <robby.simpson@ge.com>, Eliot Lear <lear@cisco.com>, Robert Collins <robertc@squid-cache.org>, Jitu Padhye <padhye@microsoft.com>, "ietf-http-wg@w3.org" <ietf-http-wg@w3.org>, "Brian Raymor (MS OPEN TECH)" <Brian.Raymor@microsoft.com>, Rob Trace <Rob.Trace@microsoft.com>, Dave Thaler <dthaler@microsoft.com>, Martin Thomson <martin.thomson@skype.net>, "Eggert, Lars" <lars@netapp.com>, Martin Stiemerling <martin.stiemerling@neclab.eu>
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Subject: Re: HTTP/2 and TCP CWND
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Hi Nandita, here are some thoughts inline: On 4/18/2013 7:55 PM, Nandita Dukkipati wrote: > Nice points Patrick. > > To me these are the high order bits for letting CWND cookie feature remain- > > * As you correctly note, apps get around the static value of initcwnd > per connection by using an arbitrarily large number of parallel > connections -- compared to this crude hammer, CWND cookie feature is a > saner way to start. I think that logic isn't considering other options. I agree this is the "less bad" of the two options you mention, but there are more than two bad ideas (and maybe even a couple good ones) to choose from. In this case, it doesn't appear that the story has yet been well put together to show that this is more helpful than harmful. There are strawman arguments in both directions, but certainly more research to be done before it could be suitable for a Internet standard. > * It's always arguable on how valid the CWND is... but then, this is > true of any starting condition. So the question really is: Is past value > from some XXX time ago less/more wrong on average than starting with an > arbitrary constant? It is a great research question, and very interesting. The things to look at are what the impact of being wrong on different granularities is, and what the likelihood of being wrong at different granularities is. > CWND-SETTING is an API which gives the transport access to long term > persistent information. As such its efficacy may be subjective without > data, so it only seems reasonable to me to let the feature remain. In an > ideal world, we would have a holistic design of a transport that > understands its application well, but short of this ideal, CWND-SETTING > is a way to take us forward. If the prior state variables can be utilized, they should be utilized by code that has a more global view of the set of simultaneous connections and other things going on in the host, and provide information to TCP for potential use. I don't think simply exporting the variable for some other unspecified code to control is a good design decision. In general though, Lars made the point that TCPM would be a good place to get rapid feedback on this ... the startup problem is well-known and has been beat upon for many years. -- Wes Eddy MTI Systems
- HTTP/2 and TCP CWND Jitu Padhye
- Re: HTTP/2 and TCP CWND Roberto Peon
- Re: HTTP/2 and TCP CWND Robert Collins
- Re: HTTP/2 and TCP CWND Patrick McManus
- Re: HTTP/2 and TCP CWND Roberto Peon
- RE: HTTP/2 and TCP CWND Gabriel Montenegro
- Re: HTTP/2 and TCP CWND Eliot Lear
- Re: HTTP/2 and TCP CWND Mark Nottingham
- Re: HTTP/2 and TCP CWND Simpson, Robby (GE Energy Management)
- Re: HTTP/2 and TCP CWND Roberto Peon
- RE: HTTP/2 and TCP CWND Gabriel Montenegro
- Re: HTTP/2 and TCP CWND Roberto Peon
- Re: HTTP/2 and TCP CWND Roberto Peon
- Re: HTTP/2 and TCP CWND Roberto Peon
- Re: HTTP/2 and TCP CWND Patrick McManus
- Re: HTTP/2 and TCP CWND Martin Nilsson
- Re: HTTP/2 and TCP CWND Roberto Peon
- Re: HTTP/2 and TCP CWND Eliot Lear
- Re: HTTP/2 and TCP CWND Simpson, Robby (GE Energy Management)
- Re: HTTP/2 and TCP CWND Roberto Peon
- Re: HTTP/2 and TCP CWND Simpson, Robby (GE Energy Management)
- Re: HTTP/2 and TCP CWND Roberto Peon
- Re: HTTP/2 and TCP CWND Wesley Eddy
- Re: HTTP/2 and TCP CWND Patrick McManus
- Re: HTTP/2 and TCP CWND Yuchung Cheng
- Re: HTTP/2 and TCP CWND Eggert, Lars
- Re: HTTP/2 and TCP CWND Nandita Dukkipati
- Re: HTTP/2 and TCP CWND Wesley Eddy
- Re: HTTP/2 and TCP CWND Eliot Lear
- Re: HTTP/2 and TCP CWND Eggert, Lars
- Re: HTTP/2 and TCP CWND Eggert, Lars
- Re: HTTP/2 and TCP CWND Peter Lepeska
- Re: HTTP/2 and TCP CWND William Chan (陈智昌)
- Re: HTTP/2 and TCP CWND Peter Lepeska
- Re: HTTP/2 and TCP CWND William Chan (陈智昌)
- Re: HTTP/2 and TCP CWND Peter Lepeska
- Re: HTTP/2 and TCP CWND William Chan (陈智昌)
- Re: HTTP/2 and TCP CWND Peter Lepeska
- Re: HTTP/2 and TCP CWND William Chan (陈智昌)
- Re: HTTP/2 and TCP CWND Peter Lepeska
- Re: HTTP/2 and TCP CWND Mark Nottingham
- Re: HTTP/2 and TCP CWND Eliot Lear
- Re: HTTP/2 and TCP CWND Yuchung Cheng